By Susannah Calderan
The SCANS-III shipboard teams have all eyes on the sea, searching for whales and dolphins. But we’re all ears too, thanks to our passive acoustic monitoring (PAM) equipment. Whilst we’re carrying out visual survey, we are also towing a hydrophone array 350m astern of our vessel, making continuous recordings at a rate of 500,000 samples per second. The array has two pairs of hydrophones covering mid and high frequencies, enabling us to detect the vocalisations of most of the whale and dolphin species we encounter.
Acoustic monitoring is especially useful in poor light or sea conditions, when visual observations are difficult. It is an excellent way of detecting the deep-diving species, which make long dives most of the time and are not often at the surface and available to be seen. They do vocalise, however, and so can be detected on the hydrophone.
A great example of this is the sperm whale, which produces loud, clear “clicks” throughout its dives. These can be detected and localised to investigate the animals’ distribution and density.
We have also been hearing pilot whales, which produce a range of distinctive clicks and whistles, often very close to the hydrophone. We’re also detecting the whistles and clicks of the smaller dolphin species.
The observer team has been fortunate enough to observe several beaked whales. Their high-frequency, highly directional clicks can be difficult to detect but we hope that in analysis of the acoustic data we will find some in our recordings.